IMAGINE it's the soccer World Cup final, but there's no TV broadcast. The sport's governing body has decided that all but a few photos will be embargoed for half a year, and that all refereeing decisions will be reviewed by experts in the months ahead before a winner is announced.

It sounds silly, but this is pretty much how many space enthusiasts had to experience the countdown to the final phase of Europe's much-anticipated Rosetta mission.

Rosetta has been travelling to its target – the comet Churyumov-Gerasimenko – for 10 years. Last month, with the probe having covered more than 6 billion kilometres, Rosetta's main camera system saw the target looming larger by the day. Yet images were released just once a week. There was no way for the public to "ride along" with the mission to one of the oldest objects in our solar system, sharing the excitement as a new frontier unfolded far from Earth.

Then on 15 July something unexpected happened. Perhaps by accident, perhaps in a moment of revolutionary fervour after Bastille Day, someone at the French space agency CNES issued sensational new images of the comet's icy core. They showed that the nucleus is in two parts, with a shape far weirder than any seen before – one now nicknamed "the rubber duck".

CNES swiftly took down the images, but by then they were all over the net. Many who saw them marvelled, including space aficionados who were incredulous that the discovery was meant to have been under wraps until the next weekly briefing.

A debate erupted on social media, and a group of German space enthusiasts sent an open letter to the mission managers, calling for full access to all images from Rosetta – a mission that is costing European taxpayers €1.3 billion. The European Space Agency (ESA) rejected the demands and insisted on a six-month moratorium on circulating mission data, images included. It said that this period had been agreed with the teams which designed and built the scientific instruments.

Such an arrangement is the norm for ground and space-based astronomical observatories and some interplanetary missions, mainly those doing in-depth mapping of planets that have already been visited.

But a spacecraft approaching an object for the first time is an entirely different story. This sort of exploration can engage us in an almost visceral way – if we have reasonable access to the adventure.

In more than 25 years of reporting on space missions, I've had the privilege of being party to some of the best "rides" into the solar system's depths. In the 1980s, NASA's Voyager encountered the gas giants, and cameras fed material live to the agency's own public TV channel for days on end. It meant the public could see these worlds up close at the same time as the scientists, sharing their excitement and puzzling with them over unexplained features.

When ESA's Giotto probe encountered comet Halley, in 1986, and comet Grigg-Skjellerup, in 1992, there were also live broadcasts for all to see.

Since the turn of the century we've had several NASA Mars landings. The nerve-jangling excitement of touchdown and the early manoeuvres were available live to anyone with a TV or computer screen. Fairly raw images from cameras on the Mars rovers are still posted online for the world to enjoy and image-processing wizards to work on. The same holds for Cassini, a joint NASA/ESA mission that has been orbiting Saturn for 10 years.

Sadly ESA has been less open on other occasions, for example the landing by its Huygens probe on Saturn's moon Titan in 2005. And it was criticised for sitting on stunning images taken by the Mars Express orbiter in 2004.

ESA counters that sharing too much data could allow someone to steal the science teams' thunder, perhaps by publishing research papers based on raw images in the public domain ahead of the teams themselves.

But nothing like this came to pass when NASA chose to share its Mars rover and Cassini orbiter images. Instead the public appreciated the chance to share in the missions and had a go at processing the images, often outdoing the pros in complex tasks such as stitching together chaotic picture sequences taken by descent cameras. Some of the results were so good that the mission teams used them in their publications. But as for the public besting the scientists in getting published in refereed journals, that never happened.

While the row over images from Rosetta's main camera system rumbled on, ESA changed its tune over images from the craft's navigational camera. ESA was initially reluctant to share these pictures, with a resolution one-fifth that of the main system, because the main camera's teams might not approve. But on 24 July it made the surprise decision, perhaps swayed by the leak from CNES and subsequent pleas, that one navigation image would be published daily.

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